Amongst such apparatus ball nuts and screws, for example, are known in the prior art, and these have small friction but also the disadvantage that the gear reduction is small, i.e. there is a large linear displacement for each revolution of the rotary movement. Devices with screws and nuts are also known, and these devices can be given a large gear reduction, i.e. a small linear displacement for each revolution of the rotary movement. However, these devices have the disadvantage that they have large friction. Apparatus of the kind described are also often expensive.
The translating apparatus in accordance with the invention combines the best properties of the described known apparatus. The apparatus thus has low friction, i.e. good efficiency, at the same time enabling a large gear reduction.
The advantages stated are achieved in that a tubular outer cylinder, comprising an outer casing at one end having a transverse portion and at the other an end wall opening, surrounds an inner cylinder arranged therein, axially displaceable through the end wall opening of the outer cylinder but unrotatable in relation thereto, said inner cylinder comprising an inner casing with a cylindrical inner surface having a helical thread or helical groove, the outer cylinder having, preferably at the transverse portion thereof, a rotatably mounted but axially undisplacable driving means comprising a drive shaft extending axially concentric with the helical groove in the inner casing, and at its end opposite to the transverse portion of the outer cylinder having at least one eccentrically disposed cylindrical journal rigidly connected to said drive shaft, said journal carrying at least one rotatably mounted but axially undisplaceable cylindrical rolling body, a profiled rolling body, the outer cylindrical surface of which has annular ridges in a plane normal to said journal, e.g. with a thread profile, formed for complementary engagement with the helix grooves in the inner casing, the object being that when the drive shaft is rotated, the ridges on the axially undisplaceable profiled rolling bodies engage with the helix groove of the unrotatable inner casing and displace the inner cylinder axially and linearly, in relation to the outer cylinder a distance and direction depending on the pitch and direction of the helical groove.
Further advantages are obtained if the eccentric journal consists of an eccentric sleeve rigidly and undistortably attached to the drive shaft, and having a hole for accomodating the drive shaft, eccentrically disposed in relation to the journalling surface.
It is also advantageous to make the profiled rolling body as a rolling bearing, the outer surface of its outer ring having complementary ridges coacting and engaging with the helix groove.
It is even advantageous to make the apparatus so that the outer ring of the rolling bearing carries a separate sleeve, the outer periphery of which has the complementary ridges, or that the driving means comprises several profiled rolling bodies evenly distributed around the centre line of the drive shaft.
Other valuable advantages are obtained by the profiled rolling bodies being arranged for axial and radial adjustment on the eccentric journals, for the purpose of allowing said bodies to be tightened against each other for eliminating axial play between said bodies of the driving system and the helical groove or thread of the inner cylinder.